It is not magic, just good engineers they had back then. IIRC that lens used some old glass that was toxic to the workers, hence a long gap between being discontinued and before the f/2 IS.
A legendary lens that if I ever find one at the right price (to compensate for the risk of ending up with a paper weight), I will grab it to complete my dream combo for my portrait work 😀
It is a great lens. I had one for several years and sold it a few years ago. It's not a fun lens to use - especially as you get older
I found, when hand holding, the balance was awkward. All that said, hands down it was the sharpest lens I ever owned and the images it produced were just a pleasure to look at.
